Tuesday, August 17, 2010

New Study Confirms No Significant Risk for Cardiovascular Diseases Among Smokeless Users

A study just released by the American Journal of Epidemiology (abstract here) confirms that smokeless tobacco use is NOT associated with a significantly increased risk of cardiovascular diseases.

Regrettably, this important finding will not dominate the headlines. Authors Hiroshi Yatsuya and Aaron Folsom chose to emphasize a partially analyzed result that vilifies smokeless tobacco, while largely ignoring the most valid estimate of smokeless risks, namely that they are only minimally elevated and not statistically significant.

The research was based on the Atherosclerosis Risk in Communities (ARIC) study, which recruited almost 16,000 people age 45-64 years in 1987-89 from Forsyth County North Carolina; Jackson Mississippi; suburbs of Minneapolis; and Washington County, Maryland. An enormous amount of information about cardiovascular risk factors was collected, and episodes of heart attacks and strokes were recorded up to 2005.

This Yatsuya study reported hazard ratios (interpreted similarly to relative risks, which are described here) for heart attacks and strokes among smokeless tobacco users compared with never users. When reporting risk due to one factor – in this case, smokeless tobacco – investigators must adjust the estimate for differences in other well-recognized risk factors that might affect the results. This is especially important for heart attacks and strokes, which have many risk factors.

The importance of such adjustments is easily explained. In this study, for example, smokeless users had a higher rate than nonusers of diabetes, a potent risk factor for heart attacks that is not related to smokeless use. Therefore, researchers use techniques to adjust the heart attack risk for smokeless tobacco users to account for the difference in the diabetes rate. This process is repeated for all the other risk factors.

After adjustment for age, sex, race, education, income, alcohol use, physical activity and smoking, Yatsuya and Folsom reported that smokeless tobacco users have a 29% excess risk of heart attacks and strokes (95% Confidence Interval, 8 – 55%). Adjusting for all of these factors is appropriate, but not complete.

After further adjusting for pipe/cigar smoking and exposure to secondhand smoke, the excess heart attack and stroke risk among smokeless users was 27% (CI = 6 – 52%). This is the only result that Yatsuya and Folsom chose to highlight in the abstract. It is still only a partial result, because they had information on many other important risk factors, such as blood pressure, use of blood pressure medicines, diabetes, weight, and serum fat levels. The result after adjustment for these factors was buried in the fine print of the paper. The excess risk dropped to 21% (CI = 0 – 45%), which is 22% lower than their touted number and not statistically significant.

Why did Yatsuya and Folsom downplay the most valid result for smokeless tobacco users? Why did the journal’s reviewers and editors not insist that Yatsuya and Folsom report the results in a fair and balanced manner? One possible answer: An unbiased report about smokeless tobacco use would not have offered these strident conclusions in both the paper and the abstract: “Current users of smokeless tobacco should be informed of its harm and advised to quit the practice. Current smokers should also be given sufficient information on safe, therapeutic methods of quitting which do not include switching to smokeless tobacco.”

Can we conclude from this study that smokeless tobacco is not associated with heart attacks and strokes? Of course not. But the most valid risk estimate is so small that the authors had to all but bury it in order to support their abstinence agenda. The bottom line for consumers is that this study confirms that smokeless tobacco use is NOT associated with a significantly increased risk of cardiovascular diseases.

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